A coma is a state of prolonged unconsciousness that can be caused by a variety of problems — traumatic head injury, stroke, brain tumor, drug or alcohol intoxication, or even an underlying illness, such as diabetes or an infection.

A coma is a medical emergency. Swift action is needed to preserve life and brain function. Doctors normally order a battery of blood tests and a brain CT scan to try to determine what's causing the coma so that proper treatment can begin.

A coma seldom lasts longer than several weeks. People who are unconscious for a longer period of time may transition to a persistent vegetative state.

Depending on the cause of a coma, people who are in a persistent vegetative state for more than one year are extremely unlikely to awaken.

The signs and symptoms of a coma commonly include:

Closed eyes

Depressed brainstem reflexes, such as pupils not responding to light

No responses of limbs, except for reflex movements

No response to painful stimuli, except for reflex movements

Irregular breathing

When to see a doctor

A coma is a medical emergency. Seek immediate medical care.

Many types of problems can cause coma. Some examples are:

Traumatic brain injuries. Traumatic brain injuries, often caused by traffic collisions or acts of violence, are common causes of comas.

Stroke. Reduced or interrupted blood supply to the brain (stroke), which may be caused by blocked arteries or a burst blood vessel, can result in a coma.

Tumors. Tumors in the brain or brainstem can cause a coma.

Diabetes. In people with diabetes, blood sugar levels that become too high (hyperglycemia) or too low (hypoglycemia) can cause a coma.

Lack of oxygen. People who have been rescued from drowning or those who have been resuscitated after a heart attack may not awaken due to lack of oxygen to the brain.

Infections. Infections such as encephalitis and meningitis cause swelling (inflammation) of the brain, spinal cord or the tissues that surround the brain. Severe cases of these infections can result in brain damage or a coma.

Seizures. Ongoing seizures may lead to a coma.

Toxins. Exposure to toxins, such as carbon monoxide or lead, can cause brain damage and a coma.

Drugs and alcohol. Overdosing on drugs or alcohol can result in a coma.

Although many people gradually recover from a coma, others enter a vegetative state or die. Some people who recover from a coma may have major or minor disabilities.

Complications may develop during a coma, including pressure sores, bladder infections, blood clots in the legs and other problems.

A coma is an emergency medical condition. If you are with a person who develops signs and symptoms of a coma, call 911 or your local emergency number immediately.

When you arrive at the hospital, emergency room staff will need as much information as possible from family and friends about what happened to the affected person before the coma. On the way to the hospital, you may be asked the following questions while riding in the ambulance:

Did the coma start abruptly or gradually?

Were there problems with vision, dizziness or numbness beforehand?

Does the affected person have any history of diabetes, seizures or strokes?

Did you notice any changes in the affected person's health in the time leading up to the coma, such as a fever or worsening headache?

Did you notice any changes in the affected person's ability to function in the time leading up to the coma, such as frequent falls or confusion?

Did the affected person use any prescription or nonprescription drugs?

Because people in a coma can't express themselves, doctors must rely on physical clues and information provided by families and friends. Be prepared to provide information about the affected person, including:

Events leading up to the coma, such as vomiting or headaches

Details about how the affected person lost consciousness, including whether it occurred suddenly or over time

Any noticeable signs or symptoms prior to losing consciousness

The affected person's medical history, including other conditions he or she may have had in the past, such as a stroke or transient ischemic attacks

Recent changes in the affected person's health or behavior

The affected person's drug use, including prescription and over-the-counter medications as well as unapproved medications or illegal, recreational drugs

Physical exam

In a physical exam, doctors will check the affected person's movements and reflexes, response to painful stimuli, and pupil size. Doctors will observe breathing patterns to help diagnose the cause of the coma. Doctors also may check the skin for signs of any bruises due to trauma.

To determine the affected person's level of consciousness, doctors may speak loudly or press on the angle of the jaw or nail bed. Doctors will watch for signs of arousal, such as vocal noises, eyes opening or movement.

Doctors will test reflexive eye movements. These tests can help determine the cause of the coma and the location of brain damage.

Doctors also may squirt ice-cold or warm water into the affected person's ear canals and observe eye reactions.

Laboratory tests

Blood samples will be taken to check for:

Complete blood count

Electrolytes, glucose, thyroid, kidney and liver function

Carbon monoxide poisoning

Drug or alcohol overdose

A spinal tap (lumbar puncture) can check for signs of infections in the nervous system. During a spinal tap, a doctor or specialist inserts a needle into the spinal canal and collects a small amount of fluid for analysis.

Brain scans

Computerized tomography (CT) scan. A CT scan uses a series of X-rays to create a detailed image of the brain. A CT scan can show a brain hemorrhage, tumors, strokes and other conditions. This test is often used to diagnose and determine the cause of a coma.

Magnetic resonance imaging (MRI). An MRI uses powerful radio waves and magnets to create a detailed view of the brain. An MRI can detect brain tissue damaged by an ischemic stroke, brain hemorrhages and other conditions. MRI scans are particularly useful for examining the brainstem and deep brain structures.

Electroencephalography (EEG). An EEG measures the electrical activity inside the brain. Doctors attach small electrodes to the scalp. Doctors send a low electrical current through the electrodes. The brain's electrical impulses are then recorded. This test can determine if seizures may be the cause of a coma.

A coma is a medical emergency. Doctors will first check the affected person's airway and help maintain breathing (respiration) and circulation. Doctors may give breathing assistance, blood transfusions and other supportive care.

Emergency personnel may administer glucose or antibiotics intravenously, even before blood test results return, in case of diabetic shock or an infection affecting the brain.

Treatment varies, depending on the cause of the coma. A procedure or medications to relieve pressure on the brain due to brain swelling may be needed.

If the coma is the result of drug overdose, doctors will give medications to treat the condition. If the coma is due to seizures, doctors will administer medications to control seizures.

Other treatments may focus on medications or therapies to address an underlying disease, such as diabetes or liver disease.

Sometimes the cause of a coma can be completely reversed and the affected person will regain normal function. But if the affected person has suffered severe brain damage, he or she may sustain permanent disabilities or may never regain consciousness. The person may enter a persistent vegetative state or become brain dead.

References

Overview of coma and impaired consciousness. The Merck Manual Professional Edition. http://www.merckmanuals.com/professional/neurologic-disorders/coma-and-impaired-consciousness/overview-of-coma-and-impaired-consciousness. Accessed July 15, 2015.

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